Saturday, June 10, 2017

Observers Track the Next New Horizons’ Target

January 1, 2019, is still several months away, however, for members of NASA's New Horizons team, it's hurtling toward them like a freight train. That's when the spacecraft will fly past the distant Kuiper Belt object 2014 MU69 at close range.

Astronomers guess that it's between 25 and 45 km (15 and 30 miles) across, but the exact size depends on the reflectivity of its surface — and that's unknown. In fact, they needed the Hubble Space Telescope to discover this incredibly dim speck (magnitude 27½) at all. It's some 6½ billion km (43.3 astronomical units) from the Sun, a third farther out than Pluto is.

The stellar "shadow" cast by 2014 MU69 took about 11 minutes to sweep across Earth,so from any given location, the star would disappear for no more than about 2 seconds.

"This object has so far proven to be impossible to detect from the ground," laments Marc Buie (Southwest Research Institute). "100% of the data we have directly on 2014 MU69 is from HST, starting with the discovery images and then onward to additional images for astrometry."

To learn more and guess less, Buie and the New Horizons team have turned to an observing technique that can be even more powerful than HST: stellar occultations. It turns out that 2014 MU69, currently drifting among the rich star fields of Sagittarius about 5° northeast of the Teapot, passes directly in front of three stars this year: June 3rd, July 10th, and July 17th. That's the good news. The bad news is that these stars are themselves very faint, and (as the maps below show) getting into the predicted tracks presents plenty of challenges.